In U.S. Pat. No. 4,347,797 there is described an automatic sewing machine incorporating a sewing head, in which the reciprocating needle bar is guidingly received in a tiltably suspended bracket in order to impart to the needle bar besides its main reciprocating movement lateral jogging motions. For this purpose a gear mechanism drivingly connected to the arm shaft is provided, in which two linkage mechanisms operating at different RPM-rates are each selectably connectable to the needle carrying bracket. Due to the transmitting ratio of 1:1 or 1:2 of the linkage mechanism selectable different movements can be generated at the needle.
A disadvantage of this gear mechanism is presented by the fact that this mechanism can be shifted resp. altered with respect to its transmitting ratio at a comparable low RPM-rate, i.e. a shifting can be carried out only up to the maximum of about 80 RPM. Furthermore, such shifting even at low RPM-rates cannot be performed noiselessly and thus not without any wear occuring at elements to be engaged. Moreover, a shifting of this gear mechanism in full operation and under full load is basically not possible.
According to a modified embodiment described in the aforementioned U.S. patent it is proposed to employ two independent drive motors in order to separately generate the two movements of the needle, i.e. the main reciprocating vertical needle movement and the lateral jogging resp. zig-zag movement of the needle. As these motors must be controlled by a computer this presents a cost consuming method.